Historically, various components for tires, such as for example tire treads, have been suggested as composites of a plurality of profiled strips prepared by various extrusion processes.
Co-extruded, multi-component rubber extrudates may conventionally be prepared by co-extruding at least two different rubber compositions by using an individual extruder for each rubber composition which individually cause an extruded rubber composition to flow through a suitable die member to, in turn cause the individual rubber compositions to controllably flow and join within the die member and exit therefrom in a profiled multi-component rubber extrudate. Such co-extrusion process to prepare a multi-component rubber extrudate for a tire, such as for example a tire tread, is well known to those having skill in such art. For example, see U.S. Pat. Nos. 5,453,238, 6,172,155, 5,843,349, 5,017,118, 5,259,746, 5,171,394, 5,147,198, and 5,030,079.
In the context of the present invention, the term “multi-layered” refers to an extruded multi-component composite, or extrudate, which features alternating layers of at least two rubber compositions which extend across the thickness of the extrudate. It is considered herein that suitable convenient methods for the manufacturing of such multi-layered tire components remain to be desired in many respects. It is believed that available techniques are usually tedious and time consuming. Historically, it is believed that a rather basic procedure involves a manual assembly of different extrudate layers, but this method is limited to simple multi-layered structures (e.g. a very low number of layers and a simple extrudate shape) and the quality of hand layered-up components may become questionable, for example, if air should become entrapped between adjacent slices. One solution for the manufacturing of multi-layered rubber component is seen from the static mixer technology (U.S. Pat. No. 3,051,453) which involves a co-extrusion of different rubber compositions to cause the rubber compositions to flow through a series of specific layering inserts. In particular, it is seen that the multiplication of rubber layers is obtained by successive bi-partitions of the rubber stream within the layering inserts. Apparently within each layering insert the incoming flow is divided into two through a “split” and “stack” process to double the number of incoming layers.
However, it is considered herein that such technology is inherently focused upon manufacturing of micro-layered components, namely very large numbers of layers of very thin, rubber compositions. The complexity of such layering equipment is considered herein to be excessive for a normal use in a high volume factory environment.
Accordingly, it is desirable to prepare a multi-layered unvulcanized rubber component in an improved manner, namely by use of a single manufacturing step, where a plurality of individual layers of different rubber compositions are created and directly combined within a single pre-former during the extrusion process.
In particular, it is desired to provide a relatively simple co-extrusion method and apparatus suitable for implementation in a factory environment and for mass production of multi-layered tire components.
In particular, it is desired to provide such process with a good control of the shape and dimensions of such rubber layers.